Several things can affect Render times, the size of 'Off-Screen Set', ie how big the set was, compared to how much was visible in the render. Levels of detail will also affect the Render Time, the more detail the longer the time. Also the Lighting can affect Render Times, the more lights, like details will slow things down, that also goes for the 'Cityscape Background'. Several 'Fixes' for that would be
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, 'Camera Cutaway' removes everything outside of the camera view, but allows lighting to be unaffected, as long as you tell it to include them. Something like a 10MB image could come out as 4 or 5MB, using 'Camera Cutaway', & is quicker than going thru the Scene 'Hiding Objects' not in view, it's also good if you want to use the 'Set' for a series of renders, saves you 'forgetting to unhide objects'.